The fish with a rainbow eye

These eyes are positively spectral. They belong to a Caribbean trumpetfish, and their many colours are created by the refraction of light.

Rays of light bend as they pass in and out of the fish's eyes, and different colours of light bend different amounts. As a result, what was previously white light splinters into bands of different colours, like a rainbow. From bottom to top in the photo, the colours in the eye follow part of the usual rainbow sequence, from orange to blue.

Like all trumpetfish, Aulostomus maculatus has a long thin body rather like that of an eel. It often swims vertically, disguising itself among vertical corals. But it also camouflages itself by swimming along the lateral lines of larger fish.

The photograph, by Randall Benton, has just won third prize in the Nature category of the World Press Photo of the Year awards 2012.